const NAMED_ENTITIES: Readonly<Record<string, string>> = {
  amp: "&",
  apos: "'",
  gt: ">",
  lt: "<",
  nbsp: " ",
  quot: "\"",
};

function decodeCodePoint(codePoint: number, fallback: string): string {
  return Number.isInteger(codePoint) && codePoint >= 0 && codePoint <= 0x10ffff
    ? String.fromCodePoint(codePoint)
    : fallback;
}

export function decodeHtmlEntities(value: string): string {
  return value.replace(/&(#x[0-9a-f]+|#[0-9]+|[a-z][a-z0-9]+);?/gi, (match, entity: string) => {
    const normalized = entity.toLowerCase();

    if (normalized.startsWith("#x")) {
      return decodeCodePoint(Number.parseInt(normalized.slice(2), 16), match);
    }

    if (normalized.startsWith("#")) {
      return decodeCodePoint(Number.parseInt(normalized.slice(1), 10), match);
    }

    return NAMED_ENTITIES[normalized] ?? match;
  });
}